Musculoskeletal Flashcards

1
Q

List enzymes which indicates myonecrosis, the time to peak serum concentration following muscle damage, their half lives and tissues they are found in.

A
  • Creatine kinase (CK): peaks within 4-6h; moderate elevations decrease to normal range in 24-48h; cardiac and skeletal muscle.- Aspartate transaminase (AST): peak at 24h; half life weeks; muscle, red blood cell, liver, other tissues. - Lactate dehydrogenase (LDH): peak at 15h.
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2
Q

What test can you perform to identify subclinical rhabdomyolysis in horses?

A
  • Exercise stress test.- 15 minutes exercise: trot/walk unfit horses, steady trot fit horses; blood sample pre and 4-6 hours post-exercise.- Normal horse: CK elevates within 3 x normal range.- Rhabdomyolysis: greater than 5 x CK elevation.
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3
Q

Describe normal and abnormal findings following electromyography in the horse

A
  • Normal muscle shows burst of activity following needle insertion then quiescence (little spontaneous elec activity unless the horse moves).- Horse with abnormalities in elec condition system of muscle or denervation of endplate show abnormal spontaneous activity e.g. fibrillation potentials, positive sharp waves. - Myopathic changes incl decrease in duration and amplitude of motor unit action potentials.
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4
Q

What are the main features and two types of myotonias found in horses.

A
  • Delayed relaxation of muscle after mechanical stimulation or voluntary contraction.- Abnormal muscle membrane excitability shared feature.1. Non-dystrophic myotonias: myotonia congenita, HYPP.2. Dystrophic myotonia: progressive dz.
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5
Q

Describe the signalment of horses most commonly affected by shivers.

A
  • Breeds: Draught horse breed, WBs, WB x, TBs.- Age: > 1yo.- Gender: male > female.- Height: >16.3hh.
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6
Q

What is aetiology of shivers?

A
  • Unknown. Proposed aetiologies incl genetic, traumatic, infectious and neurologic diseases.- No abnormalities on electromyography, indicating it is not a true myotonic condition.
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7
Q

Describe the clinical signs of shivers.

A
  • Primarily affects the HLs.- Characterised by periodic, involuntary spasms of the muscles in the pelvic region, pelvic limbs and tail which are exacerbated by backing or picking up the HLs.- HL in elevated, abducted and tailhead usually elevates concurrently and trembles.
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8
Q

Describe the clinical signs and aetiology of myotonia congenita in horses.

A
  • Signs manifest in first year of life and do not progress beyond 6-12 months of age.- Well developed musculature with bilateral bulging/dimpling of the thigh and rump muscles.- Stimulation exacerbates muscle dimpling and affected muscles may remain contracted for a minute or more.- Mild to mod pelvic limb lameness; gait abnormalities improve with exercise.- Genetic mutation identified in one New Forrest Pony w congenital myotonia: autosomal recessive c.1775A>C mutation –> substitution of aspartic acid for alanine in codon 592 of the CLCN1 protein.
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9
Q

Describe the clinical signs of myotonia dystrophica and the breeds in which it has been reported.

A
  • Severe clinical signs of myotonia that progress to marked muscle atrophy and possibly involve a variety of organs.- Retinal dysplasia, lenticular opacities and gonadal hypoplasia have been reported in 1 QH foal.- Reported in QHs, Appaloosas and Italian-bred foals.
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10
Q

How is a diagnosis of myotonia made?

A
  • Tentative dx on the basis of age and CSx.- Definitive dx: electromyography –> pathognomonic, crescendo-decrescendo, high-frequency repetitive bursts with characteristic dive-bomber sound.- Muscle biopsy histo: myotonia congenita may be normal or may demonstrate very variable type I muscle fibre dimension up to twice normal; myotonic dystrophy: ringed fibres, alterations in the shape and position of myonuclei, sarcoplasmic masses and an inc in endomysial and perimysial connective tissues, type II and II involved.
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11
Q

What is the prognosis for horses with myotonia?

A
  • Tx recommendations not possible; two reports of QH w HYPP and myotonic dystrophy responding to phenytoin.- Px variable and dependent on severity of CSx.- Mildly affected may show amelioration of signs w age.- Severely affected may have progression requiring euth.
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12
Q

Describe the aetiology of equine hyperkalaemic periodic paralysis (HYPP) and breeds affected by this disorder.

A
  • Autosomal dominant trait.- Point mutation that results in a phenylalanine/leucine substitution in a key part of the voltage-dependent skeletal muscle sodium channel alpha subunit.- QHs, American Paint Horses, Appaloosas and QH x.
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13
Q

Describe the pathophysiology of HYPP.

A
  • Mutation in voltage-dependent skeletal muscle sodium channel alpha subunit –> resting membrane potential is closer to firing than in normal horses.- The HYPP mutation results in a failure of a subpopulation of Na+ channels to inactivate when serum-K+ concentrations are inc (excessive K+ intake or exercise followed by rest) –> excessive inward flux of Na+ and outward flux of K+ –> persistent depolarisation of muscle cells and temporary weakness.
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14
Q

List the clinical signs of HYPP.

A
  • Range from asymptomatic to daily muscle fasicultations and weakness.- CSx develop by 2-3yo; normal between episodes.- CSx precipitated by high dietary K+ intake (>1.1%) e.g. alfalfa hay, molasses, elec supplements, kelp-based supplements; fasting, anaesthesia or heavy sedation, trailer rides, stress; exercise per se does not stimulate signs.- Myotonia: prolapsed nictitans, muscle fasiculations, become more generalised, exacerbated by stimulation.- Sweating.- Muscular weakness, may result in recumbency.- Horses may be tachycardic, tachypnoeic, anxious.- Dypsnoea or dysphagia, URT collapse, laryngeal paralysis.- Episodes last for 15-60mins; may cause death.
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15
Q

How do you diagnose a horse with HYPP?

A
  • Descent from sire Impressive + CSx suggestive.- Demonstrate base-pair sub in the abnormal segment of DNA encoding for the alpha subunit of the Na+ channel.- Electromyography: abnormal fibrillation potentials, complex repetitive discharges, occasional myotonic potentials, trains of doublets between episodes.- During episode CBC/MBA: hyperkalaemia (6-9mmol/L), haemoconcentration, mild hyponatraemia, n A-B balance.
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16
Q

Outline the treatment which can be administered to horses with HYPP during a clinical episode.

A
  • Mild episode: mild exercise or giving oral corn syrup or grain to stimulate insulin-mediated intraceullar mvt of K+.- Adrenaline IM (3ml of 1:1000/500Kg).- Acetazolamide 3mg/kg PO q8-12h.- Calcium gluconate 0.2-0.4ml/kg of 23% solution in 1L 5% dextrose –> inc extracellular Ca++ –> inc muscle membrane potential –> dec membrane hyperexcitability.- Dextrose 6mg/kg 5% solution +/- sodium bicarbonate 1-2mEq/kg –> enhanced intracellular movement of K+.- Tracheostomy if severe respiratory obstruction.
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17
Q

Outline the treatment which can be administered to horses with HYPP between episodes to try and reduce their occurrence.

A
  • Decrease dietary K+: feed 0.6-1.1% K+ in inc K+ excretion; acetazolamide also stabilised blood glucose and K+ by stim insulin secretion.
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18
Q

What is the prognosis for horses with HYPP?

A

In most cases manageable, but may be recurrent or fatal.

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19
Q

What species of clostridial organisms have been isolated from large animals with clostridial myonecrosis?

A
  • Chauvoei, septicum, sordelli commonly.- Occasionally novyi type B, perfringens type A, carnis.- Mixed infections common.
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20
Q

List the clinical signs of clostridial myonecrosis.

A
  • Commonly rapidly progressive with development of tremors, ataxia, dyspnoea, recumbency, coma and death within 12-24h.- Severe depression.- Fever.- Tachypnoea.- Anorexia.- Swollen muscles; usually inj site horse, usually trunk/legs and sometimes mm around vulva, tongue, diaphragm, udder in ruminants.- Skin over muscles initially hot, swollen, discoloured –> cool, insensitive, sloughs +/- crepitus.- Discharge/aspiration = malodorous serosanguinous.
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21
Q

List diagnostic test findings in patients with clostridial myositis.

A
  • CK and AST elevated; often not indicative of severity.- CBC/MBA consistant w toxaemia e.g. haemoconcentration, leukocytosis, toxic changes.- Cytology of aspirate: gram positive, spore-forming rod.- Tissue samples for direct smears, fluorescent antibody testing and anaerobic bacterial culture –> organism.
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22
Q

Describe the pathophysiology of clostridial myonecrosis.

A
  • Clostridial organisms ubiquitous in the environment.- Route of entry unknown but suspected to be direct inoculation (wound or inj) or GIT –> liver and skeletal muscle as dormant spores.- Tissue devitalisation (inj, transport, herding, handling) –> spores germinate –> rapid vegetative process –> release of exotoxins –> muscle necrosis and toxaemia.- Exotoxins vary depending on clostridial species involved; necrotising (lecithinase) and haemolysing (haemolysin) toxins appear to be of greatest importance.- C. sordelli toxins most potent –> fatal myositis.
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23
Q

Describe the epidemiology of clostridial myonecrosis in horses.

A
  • Associated w puncture wounds and IM injection sites.- IM irritating drugs implicated e.g. antihistamines, anthelmintics, phenylbutazone, flunixin meglumine.
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24
Q

Describe the necropsy findings in animals that have died from clostridial myonecrosis.

A
  • Rapid swelling and autolysis.- Bloodstained discharge from body orifices.- Engorgement of the subcutis and adj tissues with bloodstained tissue and gas bubbles.- Muscles firm, moist at periphery, lighter, drier in centre.- Odour like rancid butter.- Lungs often congested; fibrinohaemorrhagic pleuritis. - Heart, spleen and liver often friable.- C. sordelli: death often so rapid s/c gas accum is rare; see local myonecrosis, subendocardial haemorrhages in left ventricle, haemorrhage in trachea, bronchi, thymus, renal calyces; perirenal oedema, severe lung congestion.
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25
Q

Outline the prognosis and treatment of clostridial myonecrosis.

A
  • Px guarded to poor, often fatal; C. perfringens better Px.- AB: 44,000 IU/kg penicillin q2-4h until stable (1-5d) then swap to q6h or change to oral metronidazole.- Agressive surgical debridement incl fasciotomy.- Supportive care: IVFT, NSAIDs, ice boots.
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26
Q

Define muscle cramps vs muscle contractures and list aetiologies of the two.

A
  • Muscle cramps: arise from hyperactivity of motor units caused by repetitive firing of the peripheral and/or central nervous system; induced by forceful contraction of a shortened muscle, changes in ECF electrolyte composition (low Na, low K, diet, endurance exercise) and ear ticks.- Muscle contractures: painful spasms that represent a state of muscle contracture unaccompanied by depolarisation of the muscle membrane; malignant hyperthermia and some forms of exertional myopathies.
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27
Q

Describe the presentation and treatment of ear-tick associated muscle cramping.

A
  • Infestation with Otobius megnini (ear ticks).- Intermittent signs of severe muscle cramping of pectoral, triceps, abdominal or semimem/semitend lasting from minutes to hours.- Stimulation/percussion –> myotonic cramp, fall over.- CK elevated at 4,000-170,000 IU/L.- Local tx of ticks with pyrethrins and piperonal butoxide –> recovery in 12-23h.- Acepromazine may help with muscle cramps.
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28
Q

Describe the clinical presentation of acute rhabdomyolysis associated with Streptococcus equi.

A
  • Reported in QHs firm, swollen, panful epaxial and gluteal muscles –> recumbency.- Unrelenting pain necessitating euth w/in 24-48h.
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29
Q

List clinicopathologic abnormalities reported in horses with acute rhabdomyolysis associated with Streptococcus equi.

A
  • Mature neutrophilia.- Hyperfibrinogenaemia.- Marked elevations in CK 115,000-587,000 U/L.- Marked elevations in AST 600-14,500 U/L.- Titres to SeM protein are low (unless recently vaccinated).- Titres to myosin binding protein high in small number of horses tested.
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30
Q

List necropsy findings reported in horses with acute rhabdomyolysis associated with Streptococcus equi.

A
  • Large pale areas of necrotic mm. in HL and lumbar mm.- Histo: severe acute myonecrosis with a degree of macrophage infiltration.- Sublumbar muscles more severe and chronic necrosis.
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31
Q

What is the proposed aetiology of Streptococcus equi associated rhabdomyolysis?

A
  1. Toxic shock-like reaction arising from profound T-cell stimulation by streptococcal superantigens with the release of high levels of inflammatory cytokines.2. Bacteraemia with local multiplications and production of exotoxins or proteases within skeletal muscle.
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32
Q

Outline treatment and prognosis for horses with acute rhabdomyolysis associated with Streptococcus equi.

A
  • Tx w IV penicillin once CSx of strangles and myopathy –> high mortality rate.- Aggressive early tx may be successful.- Rifampin (inhibits protein synth) + penicillin.- Flush GPs and drain abscesses to dec bacterial load.- NSAIDs and high doses of short-acting corticosteroids may dec inflammatory response.- Manage pain: lignocaine, detomidine, ketamine CRI.- Deep bedding, turn q4h, sling if possible.
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33
Q

List the incidence and inciting causes of infarctive purpura haemorrhagica.

A
  • Severe form of purpura with high fatality rate; one study 3/53 cases of purpura.- Exposure to S. equi within 3 weeks of presentation.- Vaccination for S. equi.- Concurrent Salmonella infantum infection.- Titres for SeM protein may be markedly elevated.
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34
Q

List clinical signs of infarctive purpura haemorrhagica in horses.

A
  • Painful lameness with limb swelling, muscle stiffness.- +/- colic.- Petechiae.- Oral infarctions resembling ulcers.- Moderate well-demarcated limb oedema.- Local, firm intramuscular swellings.- +/- dec borborygmi and haemorrhagic gastric reflux.
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35
Q

List potential diagnostic test abnormalities in horses with infarctive purpura haemorrhagica.

A
  • Leukocytosis.- Neutrophilia with left shift and toxic changes.- Hyperproteinaemia.- Markedly elevated CK 47,000-280,000 U/L.- Markedly elevated AST 960-7,000 U/L.- Immune complexes in serum primarily composed of IgM or IgA and streptococcal M protein.- Peritoneal fluid: WNL or inc TP, NCC and RBCC.- U/S: focal hypoechoic lesions within muscle tissue.- Biopsies: palpable normal muscles WNL; swollen muscles: acute coagulative necrosis.
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36
Q

List post mortem findings in horses with infarctive purpura haemorrhagica.

A
  • Infarction of skeletal muscles, skin, GIT, pancreas and lungs.- S. equi abscessation of a lymph node.- Histo: leukocytoclastic vasculitis and acute coagulative necrosis resembling infarction in numerous tissues.
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37
Q

Outline treatment and prognosis for horses with infarctive purpura haemorrhagica.

A
  • High fatality rate.- Early recognition and aggressive tx nec for survival.- Penicillin, NSAIDs, tapering steroids over months.
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38
Q

What is the typical signalment of horses with immune-mediated polymyositis (IMM)? Are there any triggering factors?

A
  • QH bloodlines.- 16yo.- 1/3 of cases have had exposure of S. equi or resp dz.
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39
Q

What is the most prominent clinical sign of IMM?

A
  • Rapid onset of muscle atrophy, particularly affecting the back and croup muscles, accomp by stiffness and malaise.- Atrophy may involve 50% of muscle mass in 1wk.
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40
Q

List potential diagnostic test abnormalities in horses with IMM.

A
  • CK/AST: WNL or mild to moderately elevated.- Biopsy of epaxial and gluteal muscles: lymphocytic vasculitis, angular atrophy, lymphocyte myofibre infiltration, fibre necrosis with macrophage infiltration and regen.- Biopsy of semimem/semitend: may show evidence of atrophy or vasculitis but inflamm infiltrates may be absent.- Inflamm infiltrates in muscle samples contain high CD4:CD8 ratio w no evidence of IgG binding to myofibres.
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41
Q

Outline treatment and prognosis for horses with IMM.

A
  • If concurrent evidence of S. equi infection tx w ABs.- Tapering steroids over 1 month.- Avoid IM injections.- Muscle mass gradually recovers over 2-3mo.- Recurrence of atrophy is common and may require additional corticosteroid therapy.- Some horses develop residual muscle atrophy.
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42
Q

List viruses implicated in development of virus-associated myopathy and the muscle groups affected.

A
  • Muscle necrosis represents component of multiple organ system involvement.- Myocarditis: FMD, EI, EIA.- Myocarditis or skeletal muscle myositis: bovine ephemeral fever, MCF, BVD, bluetongue.- Primary muscle stiffness: EI, EHV-1.
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43
Q

Cysts of the sporozoan parasite Sarcocystis are commonly found in the heart, oesophagus and skeletal muscle of cattle, sheep, goats and horses. What clinical signs are seen with experimental heavy infestations?

A
  • Fever.- Anaemia - extravascular haemolysis and haemorrhage into many tissues.- Chronic myositis.- Muscle wasting/decreased gain.- Sometimes death.- Hair loss on the rump, neck and tail.- Abortion in sheep and goats.
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44
Q

Describe the lifecycle of Sarcocystis in different large animal species.

A
  • Carnivores = definitive host; herbivores = intermediate host - ingested carnivore faeces.- Cattle IH: S. cruzi (Canidae), S. hirsuta (Felidae), S. hominis (primates).- Horse IH: S. bertrami, S. equicanis, S. fayeri (dogs).- Sheep IH: S. ovicanis (Canidae).- Goats IH: S. capracanis (Canidae).
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45
Q

How do you diagnose sarcocystosis?

A

History, clinical signs, elevated muscles enzymes, immature cysts in muscle biopsies.

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46
Q

How do you control and treatment sarcocystosis in large animals?

A
  • Control: prevent feed contamination w carnivore faeces.- Cattle: ionophores may prevent.- Tx only likely successful if very early.- Tx: ionophore ABs or amprolium in food animals; successful tx in one horse w TMS, pyremethamine and phenylbutazone was reported.
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47
Q

Describe the aetiology and presentation of masseter muscle myodegeneration in horses.

A
  • Adult horses with selenium deficiency normal or MMM.- Acute bilateral swelling of masseter muscles, trismus, dysphagia and salivation.- Necropsy: histo evidence of bilateral symmetric lesions in masseters and muscles of FLs and HLs.- Tachycardias, arrhythmias may indicate myocardial damage.- Inc CK, AST, elevated CTn, pigmenturia.- Guarded Px but some reports of successful tx w enteral nutrition, IVFT, IM Se and oral vit E.- Without tx may –> permanent trismus due to muscular atrophy and fibrosis.
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48
Q

Describe the presentation and outcome of vitamin E-deficient myopathy.

A
  • CSx of EMND, deficiency in vit E, lacking evidence of neurogenic atrophy in the sacrocaudalis dorsalis (but does have moth-eaten staining pattern of mitochondria)- Muscle a-tocopherol conc low, serum conc variably low.- Muscle weakness could be reversible manifestation of sk m mitochondrial oxidative stress assoc w vit E defic.- Horses can recover completely w 5000IU/d vit E q >3 wk.- Could be entity to itself or predecessor to dev of EMND.
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49
Q

List toxic causes of rhabdomyolysis.

A
  • Ionophores: – Susceptibility: horses>sheep>pigs>goats>cattle.– Rhabdomyolysis and cardiomyopathies.– Incl monensin, lasolacid, naracin, salinomycin, laidlomycin.- Inj of lignocaine, diazepam, digoxin, levamisole, nitroclofene, pentazocine, thiazinamium, chloro, oxytet, ivermectin.- Organophosphate toxicosis.- Blister beetle toxicity (rarely).- Tetrachlorovinphos mini ponies (fly control agent).- Gossypol: monogastrics should not ingest feed w >200ppm gossypol, mature ruminants tolerate 20g/head/day.- Cassia (sicklepod), Eupatorium rugosum (white snakeroot), Isocoma wrightii (rayless goldenrod) –> cardiomyopathy and skeletal muscle degen; tremetone active in dried/dead plants.
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50
Q

What is the aetiology of malignant hyperthermia in the horse?

A
  • Genetic mutation in the ryanodine receptor 1 (RYR1) gene –> excessive Ca++ release from the sarcoplasmic reticulum.- QH and paints.
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51
Q

Describe clinical presentation of a 6wk old Arabian cross foal with suspected congenital centronuclear myopathy.

A
  • Normal at birth and first month of life.- Generalised weakness and muscle atrophy.- Only able to stand for 15-20mins w short, choppy gait.- Electromyography: dec insertional activity, fibrillation potentials, positive sharp waves, and complex repetitive discharges in all of the muscles examined. Amplitudes of the motor unit action potentials were subjectively dec.- Muscle histo: excessive variability in myofiber size, fibers with centrally located nuclei; electron microscopy: numerous vacuoles filled with granular debris consistent with dilatation of the t-tubular system and triads, z-line disruption and myofibrillar disarray; consistent w CNM in other spp.- Supportive care through several hospital visits but found dead in stall at 5mo of age.Ref: J. Vet. Intern. Med. 2014;28(6):1886–1891.
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52
Q

Describe clinical presentation and evidence of myocardial dysfunction in an Arabian mare with masseter myodegeneration.

A
  • 22yo Arabian mare w 2d Hx dysphagia, salivation and bilateral swelling of the masseter muscles.- Good appetite but masseters swollen and painful and mastication ineffective; HR 60bpm, PE otherwise WNL.- CBC WNL, elevated muscle and liver enzymes, marked pigmenturia, Se conc undetectable, Vit E conc WNL.- U/S: masseter mm thickened, increased muscle echogenicity and patchy blurring of the fasciae within the muscle layers = inflammation and oedema.- Tx: PBZ, dexamethasone, IM Vit E/Se, oral Vit E and methocarbabol, IV CRIs lignocaine and medetomidine –> CSx improved over week but persistent tachycardia.- 24-h Holter ECG: sinus tachycardia with sporadic supraventricular and uniform ventricular dysrhythmias, cTnI = 11.6ng/mL (ref bilateral mm atrophy; gradually able to chew and swallow and cardiac function n; discharged on day 17 on Vit E/Se, masseter mm WNL at 6mo.Ref: J. Vet. Intern. Med. 2011; 25(5):1171–1180.
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53
Q

Describe the clinical signs of congenital myotonia in goats.

A
  • ‘Fainting goats’.- CSx recognisable by 6wks of age; remain throughout life but not progressive.- Vary from stiffness after rest to marked general rigidity after visual, tactile or auditory stimulation.
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54
Q

What is the aetiology of congenital myotonia in goats?

A

Autosomal dominant mutation in the skeletal muscle chloride channel (CLCN1) that has incomplete penetrance.

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55
Q

Describe the epidemiology of clostridial myonecrosis in sheep and goats.

A
  • Most frequently associated with wounds occurring after shearing, docking and unsanitary surgical procedures.- Inc risk if dipped for parasites after shearing if dip becomes contaminated with clostridial spores.
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56
Q

Describe the aetiology of hypokalaemic myopathy in dairy cattle.

A
  • Occurs when serum K+ concentrations are
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57
Q

List the clinical signs of hypokalaemic myopathy in dairy cattle.

A
  • Severe weakness.- Recumbency.- Abnormal position of the head and neck.- Rumen hypomotility or atony.- Abnormal faeces.- Anorexia.- Tachycardia.
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58
Q

List diagnostic test findings in dairy cattle with hypokalaemic myopathy.

A
  • Serum K+
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59
Q

Outline the treatment of hypokalaemic myopathy in dairy cattle.

A
  • Tx difficult as serum K+ conc do not necessarily reflect muscle K+ conc.- KCl IV 16g/100Kg - do not exceed 0.5mEq/kg/h.- KCl PO 26-42/100Kg - do not exceed 230g PO q12h.- Tx to resolve primary cause of ketosis and anorexia.
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60
Q

What is the prognosis for survival in dairy cattle with hypokalaemic myopathy?

A

22-79%.

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61
Q

Describe the epidemiology of clostridial myonecrosis in cattle.

A
  • Cattle: 4-24mo; young colostral ABs, older acquired IR.- Animals on high planes of nutrition in excellent body condition most likely to develop dz.- C. sordelli most common in older feedlot cattle.- C. chauvoei most common in warm weather; spring to fall.- C. septicum, C. novyi and C. perfringens type A usually assoc w skin wounds e.g. inj sites, punctures, castration.- Infections in genital area can occur post-dystocia.
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62
Q

Outline a vaccination program for prevention of clostridial myonecrosis in cattle.

A
  • Multivalent bacterin toxoids containing antigens against multiple clostrididial spp incl chauvoei, septicum, novyi, sordelli, perfringens.- Initial vacc at 4-6mo, repeat, then q6-8mo.- Usually only nec up to 3yo but continue if high-risk area.
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63
Q

Describe the aetiology of nutritional myodegeneration (a.k.a. NMD, white muscle dz).

A
  • An acute myodegenerative dz of cardiac and skeletal muscle caused by a dietary deficiency of Se or Vit E.- Most common in young, rapidly growing calves, lambs, kids and foals, esp if dam was on Se-deficient diet.- In utero form –> CSx after birth.- Adult forms in cattle and horses also reported.- Se and Vit E synergistic but Se def more important.
64
Q

Describe the clinical signs of NMD.

A
  1. Cardiac form: acute signs of myocardial decompensation - depression, weakness, rapid irregular heartbeat, severe degeneration and often death within 24 hours.2. Skeletal form: slower onset, muscular weakness, stiffness, trembling, recumbency, painful muscles on palpation; if diaphragm and intercostal involved animals may show resp distress, inc abdo effort; if tongue muscles may show dysphagia.
65
Q

List clinicopathologic abnormalities associated with NMD.

A
  • Significantly elevated CK, AST and LDH and myoglobinuria during acute phase.- Foals: hyperK, hyperP, hypoNa, hypoCl.- Whole blood Se
66
Q

Describe the pathophysiology of NMD.

A
  • Destruction of cell membranes and proteins –> loss of cellular integrity.- Se and Vit E are biologic antioxidants.- During normal cellular metabolism highly reactive forms of oxygen (free radicals) are produced.- There is an important interrelationships b/w the Se and Vit E status of the animals and the level of polyunsaturated fatty acids (PUFAs) in the diet and NMD.- Full relationship not understood as no dz/dz can occur with deficiencies of Se +/- Vit E.- Active pasture growth –> high PUFAs e.g. calves just turned out on pasture –> inc risk.
67
Q

Describe the epidemiology of NMD.

A
  • Se-deficient areas found worldwide esp acid soils, those originating from igneous rock or with high sulfur content.- Different forage varies in Se content e.g. legumes take up less Se than grasses; lowest during rapid growth.- Vit E defic most common in animals fed poor-quality hay, straw, root crops, grain tx w propionic acid.- Vit E defic also in calves fed milk replacers containing fish oil, linseed oil, sybean oil, corn oil –> inc PUFAs.
68
Q

Describe the necropsy findings in animals that die of NMD.

A
  • Bilaterally symmetric myodegeneration charac by pale discolouration and dry appearance of affected muscle, white streams in muscle bundles, calcification and IM oedema.- White streaks coagulation necrosis or fibrosis and calc.- Cardiac form: LV and septum in calves, RV+LV lambs.
69
Q

Describe treatment and prognosis for animals with NMD.

A
  • Cardiac form: usually incompatible with life.- Skeletal form: px guarded, depends if complications.- Injectable Se IM or SC at label doses.- Oral Vit E: natural greater bioavailability than synthetic; 15-60mg/kg dry feed calves; 600-1800mg/day horses.- Supportive tx e.g. ABs for secondary pneumonia and decubital ulcers, nutrition, fluids.
70
Q

How can NMD be prevented in large animals?

A
  • Total ration Se up to 0.3ppm.- Salt/mineral mixes Se 90ppm for sheep, 120ppm for cattle.- Max intake Se 0.7mg/head/day for sheep, 3mg/head/day for cattle.- Se boluses not in USA, but can do 30d inj of Se/Vit E.- Horses: Se 1mg/day inc blood Se above NMD levels; recomm to supp preg mares in Se defic areas.- Periodic blood/tissue sampling for Se q 60-90d.
71
Q

Which muscle fibres are initially recruited with slow exercise and how does the fibre type change as exercise speed or intensity increases?

A

During slow exercise Type 1 fibres and a small number of Type 2a fibres predominate. As the speed or duration increases more fibres will be recruited in the order of Type 1, Type 2a and Type 2x.

72
Q

What is percussion myotonia?

A

When a muscle holds its contraction for several seconds after percussion.

73
Q

Regardless of the cause of rhabdomyolysis the final pathway is cell death due to what?

A

Aberrant calcium cycling

74
Q

What are the general mechanisms by which aberrant calcium cycling/calcium accumulation occurs?

A
  • Energy pathways that generate ATP for the Ca pump can be impaired- Ca pump or channels aren’t functioning adequately- Cell membranes becomes damaged.
75
Q

Histologically how can you differentiate neurogenic from myogenic muscle atrophy?

A

Neurogenic: involves Type 1 and Type 2 fubres, characterised by small, angular atrophied fibres.Myogenic: fast twitch fibres predominantly, characterised by anguloid atrophy.

76
Q

List differentials for muscle fasciculations.

A
  • Nerve root irritation- Electrolyte abnormalities- Weakness- Fatigue- Anxiety- Cold- Ion channel defects within the sarcolemma causing abnormal propagation of muscle cell depolarisation
77
Q

What is the normal time to peak concentration and half life of CK, AST and LDH in cases of muscle damage?

A

CK: Peaks within 4-6 hours, declines to normal within 48 hours unless elevation is above 100,000 iu/L in which case it may take relatively longer to return to normal. Indurance rides may cause increase between 1000-4000iu/L and prolonged recumbency without myopathy can result in increase to 3000iu/L.AST: Peaks within 24 hours, not muscle specific, plasma half life is 7-10 days (some sources say 7-8) so can take weeks to return to normal. LDH: Peaks within 24 hours and half life is intermediary between CK and AST - probably around 7 days. Not muscle specific.

78
Q

What is a reasonable exercise response test in a fit and an unfit horse to provoke subclinical exertional rhabdomyolysis?

A

Fit horse: walk for 3 mins then trot for 12 minsUnfit horse: alternate between 2 mins walking, 2 mins trotting. Should see less than 3 fold increase (most healthy horses show no change at this level).

79
Q

Which electrolytes should be measured as part of examination for mod-severe rhabdomyolysis or disease with muscle fasciculations as a feature?

A

Na, K, Ca, Cl and P

80
Q

In cases of atypical myopathy/hypoglycin A toxicity, what is the expected urine pH?

A

Acidic.

81
Q

Specific muscle groups are indicated for biopsy as a diagnosis of certain diseases - which ones are these?

A
  • EMND: Sacrocaudalis dorsalis medialis muscle- Hypoglycin A: Diaphragm and deep postural muscles- Recumbency from severe rhabdomyolysis: deep pelvic muscles such as iliopsoas- Immune-mediated myositis (eg in QH): gluteal or lumbar biopsy or biopsy of an atrophied muscle.
82
Q

What are the normal and abnormal findings on EMG (specifically denervation, electrical conduction defects, and myopathic changes)?

A

Normal muscle: regular wave patterns suggesting adjacent motor units are being recruited. Denervation: abnormal spontaneous electrical activity in the form of fibrillation potentials and positive sharp waves.Electrical conduction defects: complex repetitive discharges or myotonic dischargesMyopathic changes: decreased duration and amplitude of motor unit action potentials.

83
Q

What are the typical histologic findings with repetitive overtraining?

A

Increased muscle fibre size variation and centrally displaced myonuclei in muscle biopsies.

84
Q

What are the recommended provisions of dietary electrolytes for horses exercising in hot humid conditions or sweating excessively?

A

30-50gNaCl/day15-25g light salt containing KCl/dayCa : P ratio of 2:1

85
Q

What treatments may be indicated for acute rhabdomyolysis?

A
  • Rest (don’t transport for 24-48hrs) and increased susceptibility to re-injury for 2 weeks after an acute episode.- IVFT and address electrolyte and acid base derangements (typically low Na, low Cl and high K and often alkalotic- Anxiolytics such as ACP may help; also increases blood flow through vasodilation- Analgesia with NSAIDs (caution if dehydrated due to risk of renal damage, particularly with concurrent pigmenturia), Dom/Torb may also be used as analgesics if required. - IV or enteral DMSO may help as an antioxidant, anti-inflammatory and osmotic diuretic- Methylprednisolone succinate once. - Muscle relaxants such as methocarbamol may have variable results- Dantrolene may decrease release of Ca from the SR which may help reduce further aggravation of muscle contraction and necrosis but is contraindicated in HYPP due to increases in K concentration
86
Q

List examples of chronic exertional myopathies

A
  • RER- Malignant hyperthermia- PSSM (type 1 and type 2)- Idiopathic exertional rhabdomyolysis- Mitochondrial myopathy
87
Q

What is the classic signalment of horses with RER and during what kind of exercise are episodes most likely to occur?

A
  • Typically nervous temperament, SB and TB over-represented, young females over-represented- Often exercise is preceded by a day or two of rest- Usually occurs when exercise is restricted/the horse is held back (rarely occurs in horses allowed to freely gallop, hence not associated with lactic acid)
88
Q

True or false: 2yo fillies have bigger fluctuations in their CK values than 3yos?

A

True

89
Q

True or false: Abnormal amylase resistant polysaccharide has not been identified in horses with RER but increased sub-sarcollemmal amylase sensitive glycogen has been?

A

True.

90
Q

What are the rest recommendations with horses with ER?

A

If sporadic ER, rest until CK normalisesWith RER daily exercise should continue to prevent further episodes (only when CK <3000iu/L). If CK >3000iu/L then a brief period of rest may be indicated.

91
Q

What are the exercise recommendations to minimise the risk of further episodes of ER?

A
  • Interval training and reduction of job miles to <15min/session will benefit SBs- For ridden horses a relaxed warm up with intermittent long and low stretching and regular breaks to stretch.
92
Q

What are the nutritional recommendations for horses with RER?

A
  • Less than 20% of the DE should be supplied by NSC (low glycaemic diets help with a calmer demeanour and low pre-exercise HR)- At least 20% of DE should be supplied by fat (high fat diet is less about changing the muscle metabolism and probably more about reducing anxiety and exciteability which are closely linked to RER).- Low quality hay is less of an issue with TBs than QH due to less pronounced insulinaemic response to high NSC hay.- As lactic acidosis is no longer thought to be associated with RER supplements that reduce lactic acidosis are not indicated.
93
Q

What additional therapeutics can be used to reduce the impact/severity of RER?

A
  • ACP pre-exercise to reduce excitement- Reserpine and fluphenazine have longer effects although fluphenazine has been associated with extra-pyramidal effects- Dantrolene may reduce [Ca] and decrease signs of rhabdomyolysis (significantly lower CK 4 hrs post exercise in horses given dantrolene 1 hr before exercise)- Phenytoin may help prevent rhabdomyolysis by its effects on ion channels (including Na and Ca channels). However can cause drowsiness and ataxia at high doses so therapeutic monitoring and maintenance of 8ug/mL in blood is advised. * is a monoaminoxidase activator so affects [plasma] other drugs.
94
Q

What is the affected gene and mode of inheritance of malignant hyperthermia and which breeds are affected?

A
  • Exon 46 of the skeletal muscle ryanodine receptor 1 gene (RYR1)- Autosomal dominant mutation- QH and paints
95
Q

What does the RYR1 defect do in cases of malignant hyperthermia?

A

Lowers the activation and heightens the deactivation threshold of the ryanodine receptor which intermittently can result in a dramatic efflux of Ca from the sarcoplasmic reticulum, increasing cyotplasmic Ca and producting a contracture. Anaerobic glycogen metaboilsm is activated, lactate is produced and excessive heat is generated and massive muscle necrosis ensues.

96
Q

What are the common triggers for malignant hyperthermia and what concurrent defect may exacerbate the signs?

A

Rhabdomyolysis may be induced by exercise or anaesthesia (typically halothane anaesthesia). Exacerbated by a concurrent mutation of the GYS1 gene causing PSSM1.

97
Q

What are the clinical signs and cause of death in horses with malignant hyperthermia?

A
  • Hyperthermia (if develops during anaesthesia discontinue immediately and begin active cooling)- Hypercapnoea- Acidosis (treat with NaHCO3 if develops)- Haemoconcentration, increase Ca, P, glucose and creatinine- Death from cardiopulmonary arrest
98
Q

True or false: muscle biopsy is often not that useful in diagnosis of malignant hyperthermia

A

True.

99
Q

What treatments may be useful in malignant hyperthermia, particularly if anaesthesia is necessary?

A

Dantrolene 30-60 minutes before anaesthesia (unless they concurrently have HYPP in which the increased K with dantrolene makes in contraindicated).

100
Q

What is the GYS1 gene associated with, how is it inherited and which condition is this a feature of?

A

Associated with increased amylase-resistant polysaccharide in skeletal muscle. It is an autosomal dominant misense mutation resulting in higher than normal activity of glucogen synthase both t basal states and when activated by glucose-6-phosphate. The GYS1 gene has been associated with PSSM1

101
Q

In which breeds is PSSM1 common?

A
  • European drafts but less commonly Shires or Clydesdales- Irish Draught, Cob and Conemarra- QH, particularly halter horses (Type 1 accounts for 72% of QH with PSSM)- WB (Type 1 accounts for 18%)Low prevalence in light breeds
102
Q

True or false: No temperament, body type or gender predilection exists for PSSM1?

A

True

103
Q

True or false: Signs of PSSM1 most commonly occur after strenuous exercise, particularly if exercise occurs every day.

A

False. Most common at walk and trot, particularly after several days of rest.

104
Q

What are the distinctive features of PSSM1 on histology?

A

Numerous subsarcolemmal vacuoles and dense crystalline period acid-schiff (PAS) positive and amylase resistant inclusion in fast twitch fibres.

105
Q

What is the typical signalment and presenting clinical signs in horses with PSSM1?

A
  • Age of onset is 1-14 yrs, average 5yrs. - Tucked up, fasciculations on the flank, muscle stiffness, sweating, reluctance to move forward and overt firm muscle contractures- Hindlimbs more often affected .- Chronic signs include lack of energy under saddle, reluctance to move forward, stopping and stretching as if to urinate, sour attitude to exercise- Chronic back pain, reluctance to round over fences and fasciculations or pain on palpation of the lumbar muscles. - Progressive weakness and muscle loss resulting in difficulty rising may be seen in draft breeds.
106
Q

What are the defining histological features of PSSM2?

A

Not just defined by presence of amylase resistant polysaccharide but also abnormal appearance of amylase-sensitive glycogen. Muscle glycogen concentrations aren’t typically as high as those with PSSM1. Centrally located nuclei, subsarcolemmal vacuoles, muscle necrosis, macrophage infiltration of myofibres, regenerative fibres and anguloid myofibre atrophy may all be seen with PSSM2.

107
Q

True or false: Highly trained horses have increased glycogen storage as a normal response to training.

A

True

108
Q

What are the important management factors for cases of PSSM?

A
  • Provide a low NSC diet, increasing fat in the diet (unless overweight, in which case fast 6 hrs before to increase blood [FFA]) to increase the amount of nonesterfied fatty acid available for muscle metabolism, - Provide adequate time to adjust to the dietary modifications before resuming exercise- Duration rather than intensity of exercise is often more important - Exercise programme must be gradually increased and consistently performed- Minimise days without worth or some form of exercise- If an episode occurs, don’t box rest more than 48 hours, small paddock turnout (2wks) is best so they can moderate their own exercise but continue to move.
109
Q

Why is it important to reduce an insulinaemic response in horses with PSSM?

A

Insulin stimulates the already overactive glycogen synthase.

110
Q

What are the histologic features of myofibrillar myopathy and what distinguishes this condition from PPSM2.

A
  • Increased aggregates of cytoplasmic glycogen- Amylase-resistant polysaccharide in a few fibres- Centrally located myonuclei in mature myofibres- Distinguished from PSSM2 by presence of disrupted myofibrillar alignment and largem desmin and alpha-beta crystallin positive cytoplasmic aggregates in those with recent ER.
111
Q

In which breeds has myofibrillar myopathy been reported?

A

Arabians and Warmbloods - in WBs desmin positive aggregates were found in myofibres indicating a potentially heritable form (found in multiple affected generations). Muscle tissue is characterised by ectopic accumulation of desmin and Z disc and myofibrillar degeneration.

112
Q

Mitochondrial myopathy characterised by a deficiency of respiratory chain function was identified in a 3yo Arabian filly with profound exercise intolerance and normal CK post exercise. The condition was progressive. What was the defect identified in this condition?

A

Deficiency in complex 1 (nicotinamide adenine dinucleotide : ubiquinone reductase)

113
Q

What is the specific defect in glycogen branching enzyme deficiency?

A

Premature stop codon in exon 1 of the glycogen branching enzymes I gene (GBE1)

114
Q

List the clinical signs of glycogen branching enzyme deficiency and the histologic features

A
  • Abortion in 2nd or 3rd trimester or stillbirth (3% of abortions in QH and related breeds are thought to be due to this condition)- Hyperthermia at birth- Mild flexural limb deformities- Intermittent seizures- Skeletal and respiratory muscle weakness- Sudden deathHisto: Muscle, heart and liver typically show absence of PAS staining for glycogen as well as PAS positive globular or crystalline intracellular inclusions. All affected foals die.
115
Q

Nutritional myodegeneration (white muscle disease) is an acute degenerative disease affecting cardiac and skeletal muscle of young foals that are rapidly growing and born to dams that consumed vitamin E and/or Se diets during gestation - Se and Vit E appear synergistic in preventing NMD but which one is thought to be most important in the disease pathogenesis?

A

Se is thought to be most important as Se deficiency seems to contribute more to oxidant damage of muscle cell membranes.

116
Q

What are the roles of vitamin E and selenium with respect to cellular function

A

Se: key component of glutathione peroxidase that acts to destroy hydrogen peroxide and lipoperoxides that are generated during normal muscle metabolism.Vit E: acts within cell membranes as an antioxidant that scavenges free radicals that otherwise might react with unsaturated fatty acids to form lipid hydroperoxides.

117
Q

What are the typical clinical signs of foals with NMD and how does the prognosis vary with each?

A
  • Cadiorespiratory syndrome characterised by dyspnoea, rapid irregular heartbeat, weakness, recumbency and death. Prognosis is poor. - Skeletal muscle syndrome with weakness, trembling, stiffness and inability to stand for more than short periods. Tends to be more amenable to treatment.- Dysphagia due to necrosis of the tongue, often with secondary aspiration pneumonia, may be the only sign. Muscles typically affected: Tongue, gastrocnemius, semitendinosus, semimembranosis, biceps femoris, lumbar, gluteal and neck musculature.
118
Q

What are the characteristic gross necropsy and histologic findings with NMD?

A
  • Grossly muscles appear dry, pale and streaked- Histologically you may see calcification and oedema in bilaterally symmetrical muscle groups, hypercontracted and fragmented fibres
119
Q

Vitamin E deficient myopathy is similar to equine motor neuron disease and may be a predecessor. What are the distinguishing features between these conditions?

A
  • Vit E deficient myopathy lacks the hallmark neurogenic atrophy in the sacrocaudalis dorsalis medialis muscle that is seen with EMND, and instead shows myogenic features.- Vit E deficient myopathy shows characteristic alterations in mitochondrial distribution that appears to be a reversible manifestation of skeletal muscle mitochondrial oxidative stress- Vit E deficient myopathy is generally responsive to treatment with Vit E.
120
Q

What are the characteristic features of a biopsy from a horse with vitamin E deficient myopathy?

A

“Moth-eaten” staining pattern in mitochondrial stains while other muscles are normal.

121
Q

Although commonly asymptomatic, what are the clinical signs of sarcocystosis in true pathologic cases?

A

Fever, malaise, chronic muscle atrophy, stiffness and weakness, sometimes with fasciculations may be noted. Normochronic normocytic anaemia and increased CK and AST may also occur.

122
Q

What is the pathogenesis and most common isolated associated with Clostridial myositis?

A

Several Clostridia can cause it but most commonly C. perfringens. Dormant spores of Clostridia are present in the liver and muscle (original access via GIT). IM injection of irritating drugs such as NSAIDs, prostaglandins, anthelmintics and antihistamines are often implicated as the inciting cause for onset of myonecrosis.When local tissue is devitalised (eg after injection of irritant) and the appropriate anaerobic condition is created, spores may vegetate and begin exponential growth, releasing powerful exotoxins that act locally and systemically to create widespread organ dysfunction. Signs present within 48 hours and usually include depression, fever, toxaemia and tachypnoea. Can develop crepitus due to migration along fascial planes and can lead to MOD/DIC and death

123
Q

With clostridial myositis associated with C. perfringens, what are the common toxins, and which clostridial types have the highest mortality?

A

C. perfringens mostly alpha toxin which is a dermonecrotic toxin with phospholipase and sphingomyelinase activity. Although theta, kappa and mu toxins may also play a role. C. septicum, C chauvoei and C. sporogenes have high fatality rates.

124
Q

What are the two proposed mechanisms for the development of Strangles-associated myopathy?

A
  1. A toxic-shock-like reaction from profound non-specific T-cell stimulation by streptococcal superantigens with the release of high levels of inflammatory cytokines.2. Bacteraemia with local multiplication and production of exotoxins or proteases within skeletal muscle.
125
Q

what are the virulence factors associated with S. equi that account for muscle necrosis?

A
  • Proteases- An unidentified cytotoxic protein- Streptokinase- Streptolysin
126
Q

What are the clinical signs and clinical progression of S. equi myositis?

A

Often have enlarged submandibular lymph nodes or guttural pouch empyema and develop a stiff gait that progresses to markedly firm, swollen, painful epaxial and gluteal muscles. The majority of cases become recumbent, are unable to rise and develop unrelenting pain necessitating euthanasia.

127
Q

What is the pathogenesis and commonly associated pathogens with infarctive purpura haemorrhagica?

A
  • Immune complexes in the sera of horses with infarctive purpura haemorrhagica appear to be composed of IgM, IgA and Streptococcal M protein. - Complement is deposited near the immune complexes in vessel walls and may result in cell membrane destruction, cell death and vascular occlusion. Often occurs in muscles that are compressed during recumbency and progresses to involve many organs, including the GIT and MM. - Often a history of exposure to S. equi within 3 weeks previous, vaccination for S. equi, or a concurrent Salmonella infartum infection.
128
Q

What are the clinical signs and disease progression with infactive purpura haemorrhagica?

A
  • Focal firm muscle swellings in the abdominal, pectoral, adductor and tarsocrural muscles.- Reduced GIT borborygmi and haemorrhagic gastric reflux- Neutrophilia with left shift and toxic changes, hypoproteinaemia, hypoalbuminaemia, and marked increase in CK and AST. - Serum titres for M protein are usually markedly elevated. - Petechae, oral infarctions resembling ulcers, well demarcated moderate limb oedema. - Biopsies show diffuse acute coagulative necrosis with infarction of skeletal muscle, skin, GIT, pancreas and lungs often with S. equi equi abscessation of lymph nodes.
129
Q

What are the clinical findings and proposed mechanisms behind immune mediated myositis in QH and related breeds?

A
  • Malaise, rapid onset atrophy particularly affecting epaxial and gluteal muscles and a high serum CK and AST. - Muscle atrophy is rapid and may progress to include 40% of the horse’s muscle mass within a week. - Lymphocytic destruction of myofibres by CD4 and to a lesser extent CD8 cells. - Due to loss of self-tolerance of antigens expressed on muscle cells that occurs for unknown reasons after rhabdomyolysis, infection with S. equi or vaccination. - May be due to activation of otherwise inactive autoreactive T cells by either: 1 shared epitopes with an infectious agent causing antigenic mimicry; 2 microbial superantigens; 3 high concentraiton of local cytokines, 4 expression of an abnormal protein on sarcolemmal membranes.
130
Q

What are the histologic features of IMM in QH related breeds? And what is the mainstay of treatment?

A

Infiltration of myofibres with lymphocytes, lymphocytic vasculitis, anguloid atrophy of the myofibre, fibre necrosis and multinucleated giant cells. Semi-mem/semi-ten may be useful but epaxial and gluteals are best. Tx is steroids (anti-inflammatory rather than immune suppressive is probably sufficient)

131
Q

What are the presenting signs and signalment of affected horses with systemic calcinosis?

A
  • Mild fever, malaise, stiffness and loss of muscle mass mostly over the lumbar/gluteal area - presents the same as generallised IMM but progresses to weakness, inability to remain standing, respiratory distress, laminitis or GIT inflammation and diverse organ failure and death. - QH and QH related breeds and all <9yrs.
132
Q

What are the proposed mechanisms behind development of systemic calcinosis?

A

A Ca x P product >66 has been present in all cases - hyperphosphataemia can induce dystrophic calcification through several mechanisms:1. Passive calcium phosphate deposition from phosphate supersaturation in the blood. 2. An active process promoting conversion of smooth muscle cells to osteogenic cell types.3. Directly increasing parathyroid hormone secretion and transcription4. Interference with renal production of 1,25-(OH)2D levels.

133
Q

What are the histologic features of systemic calcinosis and treatment options?

A

Resembles IMM however multinucleated giant cells are consistently present and dystrophic calcification of muscle fibres is also evident. Tx should be directed at the underlying inflammatory cause. In humans steroids are thought to trigger this condition but in horses they are often used since it so closely resembles IMM.

134
Q

What is the pathogenesis of atypical myopathy?

A

Hypoglycin A is metabolised in the liver to methylenecyclopropylacetic acid (MCPA) and MCPA CoA irreversibly binds to multiple acyl CoA dehydrogenases which are enzymes that are essential for metabolism of short and medium chain fatty acids and branched chain amino acids. Accumulation of fat esters damages muscle cell membranes, and an energy deficiency arises from inability to metabolise fat.

135
Q

What are the clinical signs of atypical myopathy and recommended treatment options?

A

Clinical signs develop within 3-5 days of exposure- Muscular weakness, sweating, fasciculations, stiffness, tachycardia, tachypnoea, recumbency and myoglobinuria. - A rapid rise in RR is usually followed by collapse and death from cardiorespiratory failure- An acidic urine should make you suspicious but definitive diagnosis requires identification of serum acylcarnitines and urine organic acids and glycine conjugates typical of deficiency of multiple acyl Co-A dehydrogenases or isolation of MCPA or hypoglycin A in blood or urine. - Aggressive IVFT, anti-inflammatories, DMSO, vit E, vit C, NSAIDs.

136
Q

Which muscles are typically affected with atypical myopathy?

A

Deep postural and respiratory musculature and the myocardium.

137
Q

MAP below what level increases the risk for post anaesthetic myopathy?

A

70mmHg.

138
Q

Which muscles are most susceptible to focal post anaesthetic myopathy?

A

Muscles with dense fascia. These include triceps, deltoid, masseter, hindlimb extensors or if in dorsal, the hindlimb adductor and gluteal muscles.

139
Q

What treatments may be indicated with focal post anaesthetic myopathy and what preventatives are possible?

A

IVFT, NSAIDs, DMSO?. dantrolene 2-4mg/kg may be useful. Dantrolene pre-op may reduce the risk although reduced cardiac output is associated with higher doses, as well as maintaining blood pressure >MAP80-85mmHg.

140
Q

What are the clinical findings with generalised post-anaesthetic myopathy?

A

Systemic hypotension and hypoxaemia creates local ischaemic lesions with pathologic changes becoming generalised. Horses are often unable to rise and may struggle hence exacerbating trauma.

141
Q

What risk factors increase the chances of generalised post-anaesthetic myopathy?

A

An underlying myopathyHYPP (need to pre-med with acetazolamide or low doses of dantrolene (above 6mg/kg it causes increase [K] which is detrimental in these cases and also reduces CO)

142
Q

What is myotonia and what are the causes of it?

A

Delayed relaxation of muscle after mechanical stimulation or voluntary contraction caused by abnormal membrane exciteability. - Congenital: defects in skeletal muscle Cl channels (myotonia congenita) or Na channels (HYPP)- Acquired: spinous ear ticks (Otobius megnini)

143
Q

What are the typical findings with myotonia congenita?

A

Well muscled with mild-mod pelvic limb stiffness, most pronounced when exercise begins and diminishing with continuing exercise. Usually noted in first yr of life. Bilateral dimpling of thigh and rump muscles may be obvious and percussion dimpling occurs with tactile sitmulation (for up to 1min or more). Progression beyond 6-12mo doesn’t typically occur.

144
Q

What are the typical findings with myotonia dystrophica?

A

Also well muscled foals with stiff hindlimb gain but weanlings have more progressive multifocal muscle atrophy, hypertrophy and persistent stiffness that worsens with exercise. Retinal dysplasia, lenticular opacities and gonadol hypoplasia have been documented. Definitive diagnosis requires EMG (pathognomonic high frequency repetitive discharges that wax and wane creating dive bombers due to repetitive firing of affected muscles.

145
Q

What are the histologic features of myotonia congenita and myotonia dystrophica?

A

May be normal or may show variable fibre diameter up to 3x normal. Type 1 fibre hypertrophy or hypotrophy is reported. Pathology is more dramatic with myotonia dystrophica with ringed fibres centrally displaced myonuclei, sarcoplasmic masses and an increased endomysial or perimysial connective tissue. Fibre type grouping and atrophy of both Type 1 and Type 2 fibres are present.

146
Q

What is the pathogenesis of HYPP?

A

An autosomal codominant myotonia of QH and related breeds from the stallion ‘Impressive’. Due to a mutation in the gene encoding voltage dependent skeletal muscle Na channels (F1416L mutation in SCN4A gene encoding the alpha subunit of the Na channel). The result is these horses have resting sarcolemmal membrane potentials that are closer to firing. When the muscle cell begins to depolarise, a subpopulation of Na channels fail to inactivate, producing an excessive inward flux of Na and outward flux of K, resulting in persistent depolarisation of muscle cells, general muscle fasciculations and weakness.

147
Q

What are the clinical signs of HYPP?

A

Often big muscled horses. Clinical signs develop by 2-3yo. May show muscle fasciculations and weakness. Episodes often begin with a brief period of facial myotonia and potentially prolapse of the 3rd eyelid. Sweating and fasciculations progress over the flanks, neck and shoulders. Movement may exacerbate. In mild attacks horses remain standing but with severe attacks this may evolve to severe weakness, swaying, staggering, dog sitting and recumbency. In severe case paralysis of URT muscles may necessitate a tracheotomy. Differentiated from a seizure as horses remain conscious and alert despite recumbency. Episodes last 15-60 min after which time the horse stands and appears normal.

148
Q

What could be presenting clinical signs in a foal with HYPP?

A

Dysphagia, stridor and periodic URT obstruction.

149
Q

What are the dietary factors and general triggers that can precipitate HYPP? And what dietary management is advised.

A

Diets high in K (lucerne, molasses, kelp-based supplements) should be avoidedTriggers can include dietary changes, fasting, GA, heavy sedation, transport, stress, cold, pregnancy and concurrent disease. Not usually exercise. Dietary management: Balanced diet of 0.6-1.1% total K by weight and less than 33g K/meal. Forage analysis is advised. Pasture is good due to high water content making excessive K consumption unlikely. Oats, corn, wheat, barley and beet pulp should be fed in small meals several times/day. Soybean meal, sugar molasses or beet molasses are high in K so should be avoided.

150
Q

What clinicopathologic changes may be seen with HYPP?

A

Hyperkalaemia (6-9mEq/L)HaemoconcentrationHyponatraemia (mild)Normal acid base.

151
Q

In a horse with HYPP, if an episode is thought to be just begining, what treatment/management could be implemented to prevent worsening?

A

Provision of corn syrupMild exerciseAdrenaline (3mL of 1:1000/500kg)Acetazolamide (3mg/kg PO) - encourages renal K excretion and stimulates insulin secretionor Ca gluconate (0.2-0.4mL/kg of a 23% solution)An increase in extracellular Ca raises the muscle membrane threshold potential, which decreases membrane hyperexciteability. Can also give IV dextrose or NaHCO3 to encourage intracellular K movement.

152
Q

What are the clinical signs and pathogenesis of hypocalcaemic tetany?

A

Usually due to lactation, parturition, endurance rides or transport. - Stiff stilted gait- Muscle fasciculations (masseter, temporal muscle, triceps)- Trismus- Dysphagia- Synchronous diaphragmatic flutter- Convulsions, coma and death in severe cases.

153
Q

What are the Ca concentrations with which clinical signs are associated?

A

Below normal but >8mg/dL (2mmol/L) - exciteability5-8mg/dL(1.25-2mmol/L) - tetanic spasms and incoordination<5mg/dL (<1.25mmol/L) - recumbency, stupor. Often also see metabolic alkalosis, hypo or hypermagnesaemia and hyper or hypophosphataemia.

154
Q

What is the treatment of hypocalcaemia?

A

IV 20% calcium borogluconate - dilute 1:4 in saline and administer at a rate of 250-500mL/500kg (pre-dilution). Dilution reduces the risk of cardiotoxicity. You will normally see an ionotropic effect but alteration in rate and rhythm warrant suspending administration. If no response to the first dose, a second dose 15-30 minutes later can be given.

155
Q

What is the pathogenesis of synchronous diaphragmatic flutter?

A

Due to fluid and electrolyte imbalances disrupting the membrane potential of the phrenic nerve. It then begins to discharge in concert with atrial depolarisations with subsequent contraction of the diaphragm. Clinicopathologically you see low serum ionised calcium and hypochloraemic metabolic alkalosis which may alter the ratio of free to bound Ca (increases protein binding). Hypocalcaemia may be due to lactation, transport, endurance, primary hypoparathyroidism, digestive disturbances, furosemide and ingestion of blister beetles.

156
Q

What are the clinical signs of synchronous diaphragmatic flutter?

A

In addition to “thumps”, you may see inappropriate sweating, inappetence, fever or hyperthermia, depression and aperistalsis.

157
Q

What is the treatment of synchronous diaphragmatic flutter and how can it be prevented?

A

Supplement with Ca and Mg, as for Tx of hypocalcaemia. Prevention: Provision of Cl, K and Na during prolonged exercise may help prevent metabolic alkalosis, and supplementing Ca and Mg in those prone to SDF may be helpful. Decreasing dieetary Ca a few days before endurance work helps to stimulate endocrine homeostatic mechanisms and increase osteoclastic activity. Calcium losses in sweat are therefore overcome by release of Ca from bone stores. Horses fed lucerne may be at increased risk due to the high Ca content.